This invention relates to an automatic video intrusion detection system.
A video intrusion detection system enables a given area to be monitored to detect persons trying to enter a prohibited area, such as between two parallel spaced apart fences. For example, it may be desired to detect persons trying to enter premises without authorization or to leave an area, such as a prison compound, without authorization. It will be understood that the term "intrusion" includes escape attempts in which case the would-be escapee still "intrudes" a forbidden area.
Some existing video intrusion detection devices have proved inadequate in an outdoor environment. Apparently they are effective in a controlled indoor environment but when used outdoors suffer from a very high nuisance alarm rate. Such things as trees moving in the wind, birds, the shadows of birds, cloud shadows, blowing paper and even insects near the camera can at times trip the alarm. In addition, considerable problems exist with lighting variation (both in time and space) and during rain and snow. Thus the problem is very complex and no solution can be expected to be perfect.
U.S. Pat. No. 3,988,533 of Mick et al, issued Oct. 26, 1976, discloses a video motion and intrusion detection system which samples a large number of points in each video field, for example 16,384 points. The digitized value of the grey scale of each point is stored and then, on a subsequent field of the same type, new digitized values of the points are compared with the stored values from the previous scan. If the difference exceeds a predetermined limit, an alarm is generated. The digital information provides the basis for an alarm map which may be displayed on a monitor. The system appears to be very complicated.